Database Management Systems Set 32

Database Management Systems

Questions 311 to 320


311.
A super key is any key that uniquely identifies each
(a)   Entity uniquely                                (b) Object in a table (c) Table
(d)   Structure in a table                          (e) Column uniquely.
312.
A table can be logically connected to another table by defining a
(a)   Hyperlink                                        (b) Common attribute                             (c) Primary key
(d)   Candidate key                                 (e) Super Key.
313.
A primary key that consists of more than one field is called a
(a)   Composite key                                (b) Secondary key   (c) Group key
(d)   All of the above                                                             (e) None of the above.
314.
Which of the following statements concerning the primary key is true?
(a)   All primary key entries are unique
(b)   The primary key may be null
(c)   The primary key is not required for all tables
(d)   The primary key data does not have to be unique
(e)   For every primary key there must be a foreign key.
315.
In the context of a database table, the statement "A determines B" indicates that
(a)   Knowing the value of attribute A you can not look up the value of attribute B
(b)   You do not need to know the value of attribute A in order to look up the value of attribute
(c)   Knowing the value of attribute B you can look up the value of attribute A
(d)   Knowing the value of attribute A you can look up the value of attribute B
(e)   None of the above.
316.
A super key that does not contain a subset of attributes that is itself a super key is called a
(a)   Candidate key   (b) Primary key                                      (c) Super key
(d)   Secondary key  (e) Foreign key.
317.
A table that displays data redundancies yields ____________ anomalies.
(a)   Update             (b) Insertion                                           (c) Deletion
(d)   All of the above                              (e) None of the above.
318.
A table is in the Fourth Normal Form (4NF) if
(a)   All attributes must be dependent on the primary key, and must be dependent on each other
(b)   All attributes must be dependent on the primary key, but must be independent of each other
(c)   No row can contain two or more multivalued facts about an entity
(d)   A and C
(e)   B and C.
319.
A table where all attributes are dependent on the primary key and are independent of each other, and no row contains two or more multivalued facts about an entity, is said to be in
(a)   1NF                  (b) 2NF                   (c) 3NF                    (d) 4NF                   (e) BCNF.
320.
The basic SQL aggregate function that gives the number of rows containing not null values for the given column is
(a)   MIN                  (b) COUNT              (c) MAX                  (d) SUM                  (e) AVG.


Answers



311.
Answer : (a)
Reason : Super key is any key that uniquely identifies each entity uniquely         
312.
Answer : (b)
Reason : Common attribute is maintained to connect two tables logically
313.
Answer : (a)
Reason :        A primary key that consists of more than one field is called Composite key
314.
Answer : (a)
Reason: All primary keys are unique. 
315.
Answer : (d)
Reason : The answer is evident   
316.
Answer : (a)
Reason: The minimal set of super key is called candidate key.  
317.
Answer : (d)
Reason :        Table that displays data redundancies yields update, insertion, deletion anomalies       
318.
Answer : (e)
Reason :        The answer is evident
319.
Answer : (d)
Reason :        Answer is obvious
320.
Answer : (b)
Reason : Count function gives the number of rows containing not null values for the given column  

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